Fully differential current sensing

ABSTRACT

A current detection system includes an inductor and a detection circuit coupled across the inductor. The inductor is configured to receive an input signal that includes an input current and generate a voltage across the inductor. The current detection circuit includes a sensing network and a transconductance amplifier. The sensing network includes a capacitor and is configured to monitor a voltage across the inductor. The transconductance amplifier is configured to receive a differential voltage indicative of a voltage drop across the capacitor and output a differential output current proportional to the differential voltage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 16/425,449,filed May 29, 2019, now U.S. Pat. No. 10,746,778, issued Aug. 18, 2020;

Which claims benefits of and priority to U.S. patent application Ser.No. 15/810,245 (TI-77253) under 35 U.S.C. § 120, filed on Nov. 13, 2017,now U.S. Pat. No. 10,345,353, issued Jul. 9, 2019, the entirety of whichare hereby incorporated herein by reference.

BACKGROUND

A switch-mode power supply (SMPS) is an electronic circuit that convertsan input direct current (DC) supply voltage into one or more DC outputvoltages that are higher or lower in magnitude than the input DC supply,voltage. An SNIPS that generates an output voltage lower than the inputvoltage is termed a buck or step-down converter. An SNIPS that generatesan output voltage higher than the input voltage is termed a boost orstep-up converter.

A typical SMPS includes a switch for alternately opening and closing acurrent path through an inductor in response to a switching signal. Inoperation, a DC voltage is applied across the inductor. Electricalenergy is transferred to a load connected to the inductor by alternatelyopening and closing the switch as a function of the switching signal.The amount of electrical energy transferred to the load is a function ofthe duty cycle of the switch and the frequency of the switching signal.Switch-mode power supplies are widely, used to power electronic devices,particularly battery-powered devices, such as portable cellular phones,laptop computers, and other electronic systems in which efficient use ofpower is desirable.

In many systems, current sensing circuits are utilized to determine howmuch current is being generated by the SMPS for the load and/or whetherthe generated current may damage any components in the load. Therefore,current sensing circuits are designed to determine the amount of currentflowing through the inductor, and thus, into the load. In some examples,a current sensing circuit can generate an alert signal when the inputcurrent into the system is too high (e.g., can cause damage to theload).

SUMMARY

In accordance with at least one embodiment of the disclosure, a currentdetection system includes an inductor and a detection circuit coupledacross the inductor. The inductor is configured to receive an inputsignal that includes an input current and generate a voltage across theinductor. The current detection circuit includes a sensing network and atransconductance amplifier. The sensing network includes a capacitor andis configured to monitor the voltage across the inductor. Thetransconductance amplifier is configured to receive a differentialvoltage indicative of a voltage drop across the capacitor and output adifferential output current proportional to the differential voltage.

Another illustrative embodiment is a current detection circuit thatincludes a high side circuit coupled across an inductor and a low sidecircuit. The high side circuit includes a transconductance amplifierthat is configured to receive a differential voltage indicative of avoltage drop across the inductor and output a differential outputcurrent proportional to the differential voltage. The differentialvoltage includes a first voltage and a second voltage. The differentialoutput current includes a first output current and a second outputcurrent. The low side circuit is configured to receive the differentialoutput current and generate a signal indicative of an input current intothe filter based on the differential output current.

Yet another illustrative embodiment is a method of detecting an inductorcurrent in a system input signal. The method includes receiving, by aninductor, the input signal. The method also includes receiving adifferential voltage indicative of a voltage drop across the inductor.The method also includes outputting a differential output currentproportional to the differential voltage. The method also includesgenerating a signal indicative of the input current based on thedifferential output current.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a block diagram of an illustrative current detection systemin accordance with various examples;

FIG. 2 shows a circuit diagram of an illustrative high side circuit of acurrent detection circuit in accordance with various examples;

FIG. 3A shows a circuit diagram of an illustrative low side circuit of acurrent detection circuit in accordance with various examples;

FIG. 3B shows a circuit diagram of an illustrative low side circuit of acurrent detection circuit in accordance with various examples;

FIG. 4 shows a circuit diagram of an illustrative transconductanceamplifier of a current detection circuit in accordance with variousexamples;

FIG. 5 shows a circuit diagram of an illustrative transconductanceamplifier of a current detection circuit in accordance with variousexamples;

FIG. 6 shows an illustrative flow diagram of a method of detecting aninductor current in a system input signal in accordance with variousexamples; and

FIG. 7 shows an illustrative flow diagram of a method for generating asignal indicative of an input current in accordance with variousexamples.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, companies may refer to a component by different names. Thisdocument does not intend to distinguish between components that differin name but not function. In the following discussion and in the claims,the terms “including” and “comprising” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to . . . .” Also, the term “couple” or “couples” is intended tomean either an indirect or direct connection. Thus, if a first devicecouples to a second device, that connection may be through a directconnection, or through an indirect connection via other devices andconnections. The recitation “based on” is intended to mean “based atleast in part on.” Therefore, if Xis based on Y, X may be based on Y andany number of other factors.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of thedisclosure. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be exemplary of that embodiment, and not intended tointimate that the scope of the disclosure, including the claims, islimited to that embodiment.

Current sensing circuits are utilized to determine how much current isbeing generated or provided by a voltage source (e.g., by a SMPS) for aload and/or whether the generated current may damage any components inthe load. Therefore, current sensing circuits are designed to determinethe amount of current flowing through an inductor, and thus, into theload. In some examples, a current sensing circuit can generate an alertsignal when the input current into the system is too high (e.g., cancause damage to the load). Current sensing circuits may also measurecurrent flowing through inductors in any location in a circuit (e.g.,input stage, output stage, etc.).

Conventional current sensing circuits sense the voltage differenceacross the inductor (which includes a DC resistance component). Theseconventional current sensing circuits utilize a single-ended feedbacksense technique which is prone to transient output spikes if the inputcurrent suddenly changes because one node of the sense resistor isregulated while the other node is directly connected to the resistancecomponent of the inductor. This transient output spike can cause a falseindication of a high current. In other words, such a transient outputspike can cause the conventional current sensing circuit to trigger ahigh input current alert when the input current is actually below thealert threshold value. Therefore, many conventional current sensingcircuits require a filter in the high input current alert signal paththat can remove such a spike. However, if the input signal does containan input current above the alert threshold value, such a filter cancause the alert signal to be delayed. Furthermore, conventional currentsensing circuits may require a deliberate offset to be provided toensure that the input stage of the sense amplifier is provided thecorrect voltage polarity to convert the voltage difference into aproportional current. Therefore, it would be desirable for a currentsensing circuit that did not require a filter to remove common modesignals in the input current alert signal path and did not require anoffset.

In accordance with various examples, a current detection system isprovided that improves common mode response and rejection of common modenoise. The current detection system is fully differential in the inputstage and feedback (i.e., in the high side circuit of the system thatsenses the voltage drop across the inductor) and both nodes of the senseresistor are regulated. Because both the nodes see the same noise orcommon mode signals, the noise rejection is higher and the time constantrequirement of the filter of the alert signal path in the output stage(i.e., in the low side circuit of the system) is much lower thanconventional systems. In fact, in some embodiments, a filter is notrequired in the alert signal path in the output stage. Therefore, anyhigh current alert signal is able to be generated without the delay ofthe conventional system that includes a high time constant filter.Moreover, because the current detection circuit is fully differential inthe input stage, a specific polarity requirement is not required, unlikein conventional systems.

FIG. 1 shows a block diagram of an illustrative current detection system100 in accordance with various examples. The current detection system100 includes, in an embodiment, an inductor 102, a current detectioncircuit 104, a capacitor 110, a multi-phase buck converter 114, and aload 112. For example, a power source (e.g., a battery, an externalpower supply, etc.) generates an input signal 122 with an input current.The energy of the input current flow in the inductor 102 is stored as amagnetic field and released when the input signal 122 is disconnectedfrom the power source. The capacitor 110 acts in concert with theinductor 102 to filter the output terminal voltage of the inductor 102to generate the output voltage 124. The output voltage 124 powers, in anembodiment, a multi-phase buck converter 114. The multi-phase buckconverter 114 can step down the voltage received as part of the outputvoltage 124 to generate a load voltage 126. For example, the multi-phasebuck converter 114 can receive output voltage 124 at a relatively highvoltage (e.g., 12V) and generate load voltage 126 at a relatively lowvoltage (e.g., 5 v, 3V, etc.) to power a load 112. The load 112 may beany electric or electronic circuit.

The current detection circuit 104 is coupled across the inductor 102 andincludes, in an embodiment, a high side circuit 106 and a low sidecircuit 108. While shown in FIG. 1 and subsequent Figures as beingcoupled to inductor 102 at the input of the multi-phase buck converter114, the current detection circuit 104 can be coupled across anyinductor in any location of any circuit (e.g., across an inductor at theoutput of the multi-phase buck converter 114 prior to the load 112). Thecurrent detection circuit 104 is configured to sense (e.g., determine)the current in the input signal 122 (the input current). The high sidecircuit 106 is fully differential. More particularly, the high sidecircuit 106 takes an indication of the differential voltage drop acrossthe inductor 102 and generates a differential current signal that isproportional to the differential voltage drop. The low side circuit 108receives the differential current signal and generates a signalindicative of the input current based on the differential current signal(e.g., a high input current alert signal 126 and/or the actual amount ofcurrent in the input signal 122 (signal 128)). Because the high sidecircuit 106 is fully differential, common mode noise rejection is high.

FIG. 2 shows a circuit diagram of an illustrative high side circuit 106of current detection circuit 104 in accordance with various examples. Asshown in FIG. 2, the inductor 102 includes an inductive component 202and a resistive component 208. Voltage drop across the inductor 102 isprimarily due to the resistive component 208. The high side circuit 106includes, in some embodiments, a sensing network 220, and atransconductance amplifier 214 (e.g., an operational transconductanceamplifier (OTA)). The sensing network 220 can include a resistor 206 anda capacitor 208 in parallel with the inductor 102. The resistor 206 andcapacitor 208 form a sensing network that senses the voltage drop acrossthe inductor 102. More particularly, the resistor 206 is connected tothe input terminal of the inductor while the capacitor 208 is connectedto the output terminal of the inductor 102. Therefore, the voltage dropacross the inductor 102 is the same as the voltage drop across thecapacitor 208. In other words, the sensing network 220 is configured tomonitor a voltage across the inductor 102.

In some embodiments, the sensing network 220 also includes a negativetemperature coefficient (NTC) resistor 210 and switch 212. The NTCresistor 210 is a variable resistor that is configured to canceltemperature variation of the resistance component 204. For example, astemperature increases, the resistance in the resistance component 204 ofinductor 102 increases. Thus, to maintain a constant resistance in thesystem, the NTC resistor 210 is configured to decrease as thetemperature increases. The switch 212 is configured, in an embodiment,to open and close to sample voltage drop across the capacitor 208 inorder to determine and cancel any offset generated by thetransconductance amplifier 214.

The transconductance amplifier 214 is configured to receive thedifferential voltage 222 indicative of the voltage drop across thecapacitor 208, which in turn is indicative of the voltage drop acrossinductor 102. More particularly, the positive input of thetransconductance amplifier 214 is connected to a first terminal of thecapacitor 208 while the negative input of the transconductance amplifier214 is connected to a second terminal of the capacitor 208. Because thetransconductance amplifier 214 is fully differential, the negative inputcan be connected to either terminal of the capacitor 208 with thepositive input of the transconductance amplifier 214 being connected tothe other terminal. Hence, the differential voltage 222 is thedifference in voltage between the first voltage 224 and the secondvoltage 226.

The transconductance amplifier 214 is also configured to generate andoutput a differential output current 230 that is proportional to thedifferential voltage 222. The transconductance amplifier 214, in anembodiment, includes a sense resistor and at least two transconductanceloops (transconductance loop circuits). In such embodiments, thetransconductance amplifier 214 converts the voltage drop across thesense resistor into output differential current 230 that includes twosymmetrical currents (the first output current 232 and the second outputcurrent 234). In other words, the transconductance amplifier 214converts the voltage drop across the sense resistor into a positivecurrent (the first output current 232) and a negative current (thesecond output current 234) each of which has the same magnitude (i.e.,the first output current 232 is equal in magnitude to the second outputcurrent 234). Thus, as the differential voltage 222 increases (thedifference between the first voltage 224 and the second voltage 226increases), the first output current 232 increases and the second output234 decreases symmetrically. In this way, the high side circuit 106 isfully differential and thus, provides high common mode noise rejection.

FIG. 3A shows a circuit diagram of illustrative low side circuit 108 ofcurrent detection circuit 104 in accordance with various examples. Thelow side circuit 108, as shown in FIG. 3A, includes, in someembodiments, the operational amplifier 308, resistors 306, 310, 316,comparator 312, capacitor 318, and analog-to-digital converter (ADC)320. The amplifier 308, in some embodiments, receives the differentialoutput current 230, both the first output current 232 and the secondoutput current 234, from the high side circuit 106 and generates asingle-ended amplified voltage 322 from the differential output current230. For example, the voltage at node 352 is equal to V₃₂₆+(I−ΔI)*R₃₀₆,where V₃₂₆ is the voltage reference 326, I−ΔI is the first outputcurrent 232 and R₃₀₆ is the resistance of resistor 306. Similarly, thevoltage at node 354 is equal to V₃₂₂+(I+ΔI)*R₃₁₀, where V₃₂₂ is thesingle-ended amplified voltage 322, I+ΔI is the second output current234 and R₃₁₀ is the resistance of resistor 310. In some embodiments, theresistance of resistor 310 is equal to the resistance of resistor 306.Thus, the single-ended amplified voltage 322 can be defined asV₃₂₂=V₃₂₆−2ΔI*R₃₁₀, where ΔI is the output differential current 230. Insome embodiments, the amplifier 308 amplifies the voltage at nodes 352and 354 from 0-100 mV 0.5-1.7V through resistors 306 and 310.

Comparator 312 is, in an embodiment, configured to receive thesingle-ended amplified voltage 322 and reference voltage 326. Thereference voltage 326 corresponds with a threshold value of the inputcurrent (e.g., a predetermined and/or programmable value). In someembodiments, the threshold value is based on the current that, whenexceeded, causes damage to any of the electronic components of the load112. If the single-ended amplified voltage 322 is greater than thereference voltage 326, the comparator 312 generates an alert signal 126that indicates that the input current is greater than the thresholdvalue. However, if the single-ended amplified voltage 322 is not greaterthan the reference voltage 326, the comparator 312 does not generate analert signal 126 and/or generates a signal that indicates that the inputcurrent is not greater than the threshold value. Because common modenoise is reduced due to the fully differential nature of the high sidecircuit 106, a filter is not required to filter the single-endedamplified voltage 322 or a very small filter may be used (e.g., a filterwith a relatively low time constant). Therefore, the time needed todetect whether the input current is greater than the threshold value canbe reduced when compared to conventional architectures. In other words,any alert signal generated by the input current detection circuit 104 isgenerated with relatively (when compared to the conventional system)delay.

The single-ended amplified voltage 322 can also be received by the ADC320. In some embodiments, the resistor 316 and capacitor 318 act tofilter the single-ended amplified voltage 322 prior to the single-endedamplified voltage 322 being received by the ADC 320. The ADC 320 isconfigured to generate a digital output signal 128 that is indicative ofthe input current. More particularly, the ADC 320 can be configured togenerate a digital output signal 128 that is proportional to the inputcurrent.

FIG. 3B shows a circuit diagram of illustrative low side circuit 108 ofcurrent detection circuit 104 in accordance with various examples. Thelow side circuit 108, as shown in FIG. 3B, includes, in someembodiments, transistors 372-378 and resistor 360. In some embodiments,the each of the transistors 372-378 are n-channelmetal-oxide-semiconductor field-effect (NMOS) transistors. However, thetransistors 352-358 can be any type of transistor including p-channelmetal-oxide-semiconductor field-effect (PMOS) transistors and/or bipolarjunction transistors (BJTs). The low side circuit 108 receives the firstoutput current 232 and second output current 234 (differential current230) from the high side circuit 106. The low side circuit 108, utilizesthe transistors 372-378 and resistor 360 to generate an output voltage380 that is proportional to the current through the inductor 102.

FIG. 4 shows a circuit diagram of an illustrative transconductanceamplifier 214 of current detection circuit 104 in accordance withvarious examples. As discussed above, the transconductance amplifier 214can include two transconductance loop circuits as shown in FIG. 4. Thetransconductance loop circuits include, in an embodiment, transistors404-410, and sense resistor 402. The transistors 404-410 are, in anembodiment, NMOS transistors. However, the transistors 404-410 can beany type of transistor including PMOS transistors and/or BJTs.

In some embodiments, the gate of transistor 404 is configured to receivethe first voltage 224 while the gate of transistor 408 is configured toreceive the second voltage 226. However, because the high side circuit106 is fully differential, the gate of transistor 404 can receive eitherthe first voltage 224 or the second voltage 226 while the gate oftransistor 408 receives the other of the first voltage 224 or the secondvoltage 226. The source of transistor 404 is connected to the drain oftransistor 406 while the drain of transistor 404 is connected to thegate of transistor 406. The source of transistor 408 is connected to thedrain of transistor 410 while the drain of transistor 408 is connectedto the gate of transistor 410. The sense resistor 402 is connected tothe source of the first transistor 404, the drain of the transistor 406,the source of transistor 408, and the drain of transistor 410.

Because the first voltage 224 and second voltage 226 are received, in anembodiment, directly from the capacitor 208, there is no single-endedconversion of the differential voltage 230 and there is no processing ofthe differential voltage 230 prior to being received by thetransconductance amplifier 214. If the first voltage 224 is greater thanthe second voltage 226, the difference in voltage is reflected onto thesense resistor 402, hence, allowing the sense resistor 402 to measurethe voltage drop across the capacitor 208 and thus, the inductor 102.Whatever noise is in the first voltage 224 and second voltage 226translates at the same time onto the sense resistor 402. The currentthrough the sense resistor 402 is then output as first output current232 and second output current 234. In other words, the current throughsense resistor 402 is dependent and proportional to the input current.Thus, the differential current 230 is generated directly from readingthe differential voltage 222. In summary, the transconductance amplifier302 shown in FIG. 4 allows a difference in voltage across capacitor 208to be translated into a difference in current.

FIG. 5 shows a circuit diagram of an illustrative transconductanceamplifier 214 of current detection circuit 104 in accordance withvarious examples. The transconductance amplifier 214 shown in FIG. 5 issimilar to the transconductance amplifier shown in FIG. 4 and operatesin a similar manner. However, the transconductance amplifier 214 shownin FIG. 5 includes a cascoded stage that enables a larger increase ingain in the differential voltage 222 and reduces channel lengthmodulation effects of the input devices. Thus, the transconductanceamplifier 214 shown in FIG. 5 includes, in an embodiment, the senseresistor 502, the transistors 504-532 and the capacitors 534-536.Similar to transistors 404-410, the transistors 504-532 are, in anembodiment, NMOS transistors; however, in alternative embodiments, thetransistors 504-532 can be any type of transistor including PMOStransistors and/or BJTs. This architecture allows the transconductanceamplifier 214 to generate the first output current 232 and the secondoutput current 234.

FIG. 6 shows an illustrative flow diagram of a method 600 of detectingan inductor current in a system input signal in accordance with variousexamples. Though depicted sequentially as a matter of convenience, atleast some of the actions shown can be performed in a different orderand/or performed in parallel. Additionally, some embodiments may performonly some of the actions shown. In some embodiments, at least some ofthe operations of the method 600, as well as other operations describedherein, are performed by the inductor 102, the high side circuit 106 ofthe current detection circuit 104 (including the resistor 206, thecapacitor 208, the NTC resistor 210, the switch 212, and/or thetransconductance amplifier 214), and/or the low side circuit 108 of thecurrent detection circuit 104 (including the amplifier 308, theresistors 306, 310, 316, the comparator 312, the capacitor 318, and/orthe ADC 320), and implemented in logic.

The method 600 begins in block 602 with receiving, by an inductor, aninput signal. For example, the inductor 102 can be configured to receivethe input signal 122 from a voltage source or any other source. Theinput signal 122 includes an input current. In block 604, the method 600continues with receiving a differential voltage indicative of a voltagedrop across the inductor. For example, the transconductance amplifier214 can receive the differential voltage 222 from across the capacitor208. The differential voltage across capacitor 208 is indicative of thevoltage across the inductor 102; therefore, the differential voltage 222is also indicative of the voltage across the inductor 102.

The method 600 continues in block 606 with outputting a differentialoutput current that is proportional to the differential voltage. Forexample, the transconductance amplifier 214 can generate thedifferential output current 230 from the current through sense resistor402 and/or 502 which is proportional to the differential voltage 222. Inblock 608, the method 600 includes generating a signal indicative of theinput current based on the differential output current.

FIG. 7 shows an illustrative flow diagram of a method 700 of generatinga signal indicative of an input current in accordance with variousexamples. Though depicted sequentially as a matter of convenience, atleast some of the actions shown can be performed in a different orderand/or performed in parallel. Additionally, some embodiments may performonly some of the actions shown. In some embodiments, at least some ofthe operations of the method 700, as well as other operations describedherein, are performed by the inductor 102, the high side circuit 106 ofthe current detection circuit 104 (including the resistor 206, thecapacitor 208, the NTC resistor 210, the switch 212, and/or thetransconductance amplifier 214), and/or the low side circuit 108 of thecurrent detection circuit 104 (including the amplifier 308, theresistors 306, 310, 316, the comparator 312, the capacitor 318, and/orthe ADC 320), and implemented in logic.

The method 700 begins in block 702 with receiving a differential outputcurrent. For example, the amplifier 308 can receive the differentialoutput current 230 from the high side circuit 106. In block 704, themethod 700 continues with generating a single-ended amplified voltagecorresponding to the differential output current. For example, theamplifier 308 can generate single-ended amplified voltage 322.

The method 700 continues in block 706 with comparing the single endedamplified voltage to a reference voltage. For example, the comparator312 can compare the single-ended amplified voltage 322 with thereference voltage 326. In block 708, the method 700 continues withdetermining whether the reference voltage is less than the single-endedvoltage. If in block 708, a determination is made that the referencevoltage is less than the single-ended voltage, then the method 700continues in block 710 with generating an alert signal. For example, thecomparator 312 can generate alert signal 126 if the comparator 312determines that the reference voltage 326 is less than the single-endedvoltage 322. However, if, in block 708, a determination is made that thereference voltage is not less than the single-ended voltage, then themethod 700 continues in block 702 with receiving a differential outputcurrent.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present disclosure. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. A switch mode power supply comprising: a powerinput and a return ground; an inductor having a first terminal coupledto the power input and having a second terminal; a first capacitorhaving a first terminal coupled to the second terminal of the inductorand having a second terminal coupled to the return ground; a multiphasebuck converter having an input coupled to the second terminal of theinductor and having a load output; a current detection circuitincluding: a second capacitor having a first terminal coupled to thefirst terminal of the inductor, and a second terminal coupled to thesecond terminal of the inductor; and a transconductance amplifier havinga first input coupled to the first terminal of the second capacitor,having a second terminal coupled to the second terminal of the secondcapacitor, having a first current output and having a second currentoutput; and an alert signal output coupled to the first current outputand the second current output.
 2. The switch mode power supply of claim1 including a resistor coupled in series with the second capacitorbetween the second capacitor and the first terminal of the inductor. 3.The switch mode power supply of claim 1, wherein the transconductanceamplifier includes a transconductance loop circuit.
 4. The switch modepower supply of claim 3, wherein the transconductance amplifier includesa cascoded stage to increase gain of the differential voltage.
 5. Theswitch mode power supply of claim 1 including a low side circuit havinga first current input coupled to the first current output, having asecond current input coupled to the second current output, and havingthe alert signal output.
 6. The switch mode power supply of claim 5 inwhich the low side circuit includes: a reference voltage input; anoperational amplifier having a first input coupled to the first currentinput, having a second input coupled to the second current input, and anamplified output; and a comparator having a first input coupled to theamplified output, a second input coupled to the reference voltage input,and an output coupled to the alert signal output.
 7. The switch modepower supply of claim 5 in which the low side circuit includes an analogto digital converter having an input coupled to the amplified output andhaving a digital output.
 8. The switch mode power supply of claim 7including a resistor and capacitor network coupled to the input of theanalog to digital converter.
 9. A switch mode power supply comprising: apower input and a return ground; an inductor having a first terminalcoupled to the power input and having a second terminal; a firstcapacitor having a first terminal coupled to the second terminal of theinductor and having a second terminal coupled to the return ground; amultiphase buck converter having an input coupled to the second terminalof the inductor and having a load output; a current detection circuitincluding: a high side circuit coupled across the inductor, the highside circuit including: a transconductance amplifier configured toreceive a differential voltage indicative of a voltage drop across theinductor and output a differential output current proportional to thedifferential voltage, the differential voltage including a first voltageand a second voltage and the differential output current including afirst output current and a second output current; and a low side circuitconfigured to receive the differential output current and generate asignal indicative of an input current into the filter based on thedifferential output current.
 10. The switch mode power supply of claim9, in which the transconductance amplifier includes a transconductanceloop circuit.
 11. The switch mode power supply of claim 10, in which thetransconductance loop circuit includes a cascoded input stage.
 12. Theswitch mode power supply of claim 9, in which the transconductanceamplifier includes: a first transistor having a first drain, a firstgate, and a first source, the first gate configured to receive the firstvoltage; a second transistor having a second drain, a second gate, and asecond source, the second gate configured to receive the second voltage;a third transistor having a third drain, a third gate, and a thirdsource, the third drain connected to the first source and the thirdsource generating the first output current; and a fourth transistorhaving a fourth drain, a fourth gate, and a fourth source, the fourthdrain connected to the second source and the fourth source generatingthe second output current.
 13. The switch mode power supply of claim 12,in which the transconductance amplifier includes a sense resistorconnected to the first source, the second source, the third drain, andthe fourth drain.
 14. The switch mode power supply of claim 9, in whichthe low side circuit includes an operational amplifier configured toreceive the first output current and the second output current andgenerate a single-ended amplified voltage.
 15. The switch mode powersupply of claim 14, in which the low side circuit includes a comparatorconfigured to receive the single-ended amplified voltage, compare thesingle-ended amplified voltage to a reference voltage, and generate analert signal that indicates that the input current is greater than athreshold value in response to the single-ended amplified voltage beinggreater than the reference voltage, the reference voltage correspondingwith the threshold value.
 16. The switch mode power supply of claim 15,in which the comparator is configured to receive the single-endedamplified voltage directly from the operational amplifier without thesingle-ended amplified voltage being filtered.